Sweep forming assembly and method

ABSTRACT

A method and apparatus produces a roll formed bumper member comprising of a metal material. The bumper member has a predetermined transverse cross section and a predetermined curvature. A strip bumper structure is fed into a forming assembly along a line level. The bumper structure has the predetermined transverse cross section and an essentially straight longitudinal configuration. The forming assembly has a driven support roller and a pair of driven cooperating flexing rollers. A first roller of the pair of flexing rollers is positioned to deflect the bumper structure out of the line level. A second roller of the pair of flexing rollers is mounted to revolve about the first roller. The support roller and the pair of cooperating flexing rollers are driven for feeding the bumper structure between the pair of cooperating and counter rotating flexing rollers. Revolving the second flexing roller about the first flexing roller flexes the bumper structure between the support roller and the first flexing roller imparting a permanent longitudinal curvature to the bumper structure.

FIELD OF THE INVENTION

[0001] The present invention relates to vehicle bumpers and methods forproducing the same.

BACKGROUND OF THE INVENTION

[0002] Motor vehicles are typically provided with front and rear bumpersto protect the vehicle in the event of impact. Vehicle bumpers aretypically formed from a strip of sheet steel that is shaped by rollforming in a roll forming assembly to have a predetermined transversecross section that rigidifies the bumper and resists deformation duringimpact. Bumpers are also provided with a predetermined curvature in thelongitudinal direction to provide a bumper that conforms to the shape ofthe vehicle in the “cross car” or side-to-side direction.

[0003] The degree of longitudinal curvature of the bumper is referred toas bumper “sweep” in the industry. The degree of bumper sweep is ageneral measure of the radius of curvature of the bumper. A basiccommercial quantitative description of bumper sweep is obtained bymeasuring a chord length of 60 inches (1.524 m) along the bumper anddetermining the maximum distance between the bumper and the chord alonga line perpendicular to the chord. The distance is measured in inches(centimeters) and converted to a sweep number by determining the numberof eighths of an inch (0.3175 cm) in the measured distance.

[0004] Bumpers in commercial use typically have sweeps of approximatelyzero (i.e., a substantially straight bumper) up to approximately 50,although bumpers having a sweep as high as 80 are used in vehicleconstruction.

[0005] It is well known that the primary objectives of vehicle partsmanufacturers is to produce high strength bumpers that resistdeformation during impact, but that are also relatively light weight.The goal of minimizing weight can be achieved by reducing the thicknessor gauge of the bumper, thereby using less metal to construct thebumper. Minimizing vehicle weight is important because lighter weightvehicles are easier to transport prior to sale and are more fuelefficient for the vehicle owner. The manufacturer can reduce metalthickness and still meet safety requirements by using higher strengthsteel to construct the bumper.

[0006] The type of metal used for bumper construction is thus a majordeterminant of bumper weight. Most commercial bumpers, however, areconstructed of relatively mild grades of steel because mild steel gradesare easier for the parts manufacturer to sweep form during manufacture.High strength low alloy (HSLA) grade steel is an example of such a gradeof steel widely used commercially for bumper construction.

[0007] HSLA steel is available in grades having a KSI minimum yieldstrength of from 35 up to 80 (i.e., a MPa minimum yield strength of from240 to 550). Grades of steel above HSLA are also commercially available,including dual phase and martinsitic grades of steel, but most partsmanufacturers are generally not able to produce a satisfactorycommercial bumper with a significant degree of bumper sweep using thesehigher steel grades.

[0008] Martinsitic steel having a tensile strength of up to 220 KSI(1516 MPa) is commercially available. Generally, any steel having a KSIgreater than 80 (240 MPa) can be considered an ultra high strengthsteel. The rigidity and structural strength provided to the bumper bythe transverse cross section makes the sweeping process difficult andlimits the strength of the steel most manufacturers can use to constructthe bumper.

[0009] More particularly, during manufacturing, a strip of sheet steelis roll formed in a series of pairs of roll forming rollers thatgradually shape the steel in a transverse direction to provide thepredetermined transverse bumper cross section. An initially shapedbumper structure emerges from a position of exit of the roll formingassembly as an elongated, longitudinally straight, continuous structure.Typically, the initially formed bumper structure is provided with thedesired degree of longitudinal curvature (the terms “bumper sweep” and“longitudinal curvature” are used interchangeably in the presentapplication) immediately after the roll forming operation in a separatesweep forming assembly positioned at the position of exit of the rollforming assembly.

[0010] The initially shaped bumper structure emerges from the sweepforming assembly as a finally shaped continuous bumper structure. By“finally shaped” it is meant that the desired degree permanent curvaturehas been imparted to the bumper structure in both the transverse andlongitudinal directions so that the bumper structure has thepredetermined transverse bumper cross section and the predeterminedlongitudinal curvature. The finally shaped bumper structure is then fedinto a cutting assembly positioned immediately downstream of the sweepforming assembly. The cutting assembly cuts the finally shaped bumperstructure into individual bumper members of predetermined length, eachbumper member thus having the predetermined transverse bumper crosssection and the predetermined longitudinal curvature.

[0011] Known prior art sweep forming assemblies are not commerciallyusable to provide a wide range of bumper sweep when high strength steelis used to construct the bumper because they use either what iseffectively a form of extrusion or a bending operation to impart bumpersweep. One prior art method, for example, of providing bumper sweep usesa series of blocks, each block having a central opening that isgenerally the same size and shape as the transverse cross section of thebumper structure. The series of blocks is positioned so that theinitially shaped bumper structure passes through the openings as itmoves out of the roll forming assembly in the downstream direction.Selected blocks are raised so that the path formed by the openings isnot straight, thereby requiring the bumper structure to deform in thelongitudinal direction as it is forced through the openings. A degree ofpermanent curvature is thereby imparted to the bumper structure.

[0012] This method is, in effect, a form of extrusion and has severaldisadvantages. The metal-to-metal sliding engagement between the bumperstructure and the sides of the openings in the blocks wears the metal ofthe bumper structure and the metal of the blocks. The metal-to-metalsliding engagement limits the speed at which the bumper structure canpass through the assembly line and thus limits the production capacityof a manufacturing plant. This method will provide only a limited degreeof sweep and is not commercially feasible for high strength steel bumpermanufacturing.

[0013] Another sweep forming assembly which has been used commerciallyin the past several years utilizes a series of longitudinally spacedmovable upper rollers and a series of longitudinally spaced fixed lowerrollers that cooperate to bend the bumper structure after it is rollformed. The lower rollers are disposed below the advancing bumperstructure and support the same. The upper rollers are disposed above theadvancing bumper structure and are vertically movable. The rollers arearranged so that one upper roller is vertically centered between twolower rollers. The sweep is imparted by moving the upper rollersvertically downwardly into engagement with an upper surface of theadvancing initially shaped bumper structure. The upper rollers exert adownward force on the bumper structure sufficient to bend the bumperstructure between an associated pair of lower fixed rollers, therebyimparting a degree of sweep to the bumper structure.

[0014] The method performed by this assembly is not effective whenharder grades of steel are used in bumper structure construction becausehard steel grades require forces of great magnitude to bend the steel.These high magnitude bending forces are undesirable because when a forceof sufficient magnitude to bend the hard steel is applied by the upperrollers, the upper rollers tend to permanently deform the predeterminedbumper cross section of the bumper structure. More particularly, thevertical sides of a hard steel bumper structure tend to puckeruncontrollably, crease or tear under the bending force of the upperrollers. Bending operations also do not provide uniform longitudinalbumper curvature when harder grades of steel are used.

[0015] Another sweep forming assembly that bends the advancing bumperstructure to impart bumper sweep is disclosed in U.S. Pat. No.4,530,226. The '226 sweep forming assembly includes three formingstations mounted on a base assembly positioned at the end of a rollforming assembly. Each station includes a pair of cooperating formingrolls. The middle station also includes an idler roller longitudinallyspaced from the pair of forming rolls. The bumper in the '226 assemblyis permanently deformed to introduce a bumper structure primarily by theinteraction of the rollers in the middle station. The first and thirdstations primarily guide the bumper structure through the middlestation.

[0016] The pair of forming rollers and the idler roller of the middlestation of the '226 assembly are longitudinally spaced and transverselyoff-set from one another (where “transversely” is defined with respectto the bumper structure and refers to a direction perpendicular to thelongitudinal extent thereof) to permanently deform the elongated bumperstructure in the transverse direction. Specifically, the pair of formingrollers drive the bumper structure over the transversely offset singleidler roller which is fixedly mounted on the middle station downstreamof the paired forming rollers thereof. The paired forming rollers ofeach of the three stations are positioned so that the center line ofeach forming station (i.e., a line between the axes of rotation of eachpair of forming rollers) is maintained in a generally perpendicularrelationship with the tangential path of the bumper structure as itpasses longitudinally through the three forming stations. Thus, opposingtransversely directed forces are applied to the bumper structure betweenthe paired rollers of the middle station and the idler roller of themiddle station of the '226 assembly which bend the portion of the bumperstructure therebetween to impart sweep. The '226 assembly utilizesopposing transversely directed forces applied to the bumper structure atlongitudinally spaced positions to create a bending force applied alongthe portion of the bumper structure between the forming rollers of themiddle station and the idler roller of the middle station to impartsweep. Thus, the '226 assembly can impart only a limited degree of sweepand is not suited to providing sweep in high strength metals such asmartinsitic grades of steel. The '226 assembly is used to impart a sweepup to approximately 30 in a bumper constructed of HSLA steel. Otherexamples of assemblies for sweep forming bumpers are shown in referencesU.S. Pat. Nos. 4,354,372 and 5,813,594.

[0017] It is well known that every metal material has a characteristicmodulus of elasticity and that if a metal material such as steel isdeformed within its elastic limits by applied forces, the metal materialreturns to its original shape when the forces are removed. Permanentcurvature is only imparted to a metal material if it is deformed beyondits elastic limit. Prior art sweep forming assemblies such as the '226assembly are unsuccessful at sweep forming high strength steel primarilybecause they rely on a bending force to deform the steel beyond itselastic limit A bending force is a force exerted over a substantiallength of a bumper structure to impart sweep. In the '226 assembly, thebending force is exerted along the length of the bumper structurebetween the paired rollers and the idler roller of the middle station.Bending forces are ineffective at imparting large degrees of sweep tobumper structures constructed using high grades of steel because thesegrades of steel require such a high degree of force to deform beyondtheir elastic limits that the bumper structure will uncontrollablypucker or tear, rendering the bumper structure unusable.

[0018] An individual bumper is primarily intended as a protectivestructure on the vehicle. Thus, it is essential that the structure ofeach commercially produced bumper be uniform and that there be nocreasing, tearing or uncontrolled puckering of its walls to ensurecrashworthiness. It is thus essential that the transverse cross sectionof each bumper not be deformed during the sweep forming operation. Priorart sweep forming assemblies are not able to reliably impart a highdegree of sweep to bumpers constructed of relatively high grades ofsteel such as dual phase and martinsitic grades. A need exists for asweep forming assembly that can provide a bumper sweep of up toapproximately 80 for roll formed bumpers constructed of high strengthsteel such as dual phase or fully hardened martinsitic grades of steelhaving a tensile strength of up to 220 KSI (1516 MPa).

SUMMARY OF THE INVENTION

[0019] To meet the need identified above, the present invention providesa method for producing a roll formed bumper comprising of a metalmaterial and having a predetermined transverse cross section and apredetermined curvature. A bumper structure is fed into a formingassembly along a line level. The bumper structure has the predeterminedtransverse cross section and an essentially straight longitudinalconfiguration. The forming assembly has a driven support roller and apair of driven cooperating flexing rollers. A first roller of the pairof flexing rollers is positioned to deflect the bumper structure out ofthe line level and a second roller of the pair of flexing rollers ismounted to revolve about the first roller. The support roller and thepair of cooperating flexing rollers are driven for feeding the bumperstructure between the pair of cooperating and counter rotating flexingrollers. Revolving the second flexing roller about the first flexingroller flexes the bumper structure between the support roller and thefirst flexing roller imparting a permanent longitudinal curvature to thebumper structure.

[0020] Another object of the present invention is to provide a vehiclebumper constructed of a metal material. The metal material is rollformed to provide an elongated bumper structure having a predeterminedtransverse cross section and a longitudinal extent. The predeterminedtransverse cross section has one at least partially open side. Thelongitudinal extent of the bumper structure has a predetermined bumpercurvature of about 80 and the metal material has a KSI of at leastapproximately 120 (an MPa of approximately 827). Preferably the metalmaterial is a steel that has a minimum 0.2 percent offset yield strengthof about 120,000 psi (827 MPa) and a ferritic grain structure. Morepreferably, the metal material is a quenched and tempered steel having aminimum ultimate tensile strength of about 140,000 psi (965 MPa) and agrain structure comprised of ferrite and tempered martinsite. Mostpreferably, the metal material is a martinsitic steel. A preferredmartinsitic steel is a quenched and tempered steel having a minimumultimate tensile strength of from about 190,000 to about 220,000 psi(from about 1310 MPa to about 1516 MPa) and having an entirely temperedmartinsite grain structure. When this preferred martinsitic steel isused, preferably the thickness of the metal material is within the rangeof approximately 0.8 mm to approximately 1.6 mm and is more preferablywithin the range of approximately 1.0 mm to approximately 1.3 mm.

[0021] Another object of the present invention is to provide an assemblythat will carry out the method previously described, by providing adriven support roller positioned to receive a strip bumper structure ata line level. A driven first flexing roller is positioned to deflect thebumper structure from the line level and a driven second flexing rollercooperates with the first flexing roller for counter rotating therewith.The second flexing roller is movably mounted to revolve about the firstflexing roller. An adjustment assembly operably engages the secondflexing roller to effect the revolving movement of the second flexingroller about the first flexing roller. The revolving movement effectsengagement of the second flexing roller with the bumper structurebetween the support roller and the first flexing roller and urges thebumper structure against both the support roller and the first flexingroller to impart a permanent longitudinal curvature to the bumperstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 shows a sweep forming assembly constructed according to theprinciples of the present invention and shows a fragmentary portion of acontinuous strip bumper structure extending through the assembly;

[0023]FIG. 2 shows a view of the sweep forming assembly FIG. 1 in asecond adjusted operating position;

[0024]FIG. 3 shows a cross sectional view of the strip bumper structureof FIG. 1 taken through the line 3-3;

[0025]FIG. 4 shows a cross sectional view of the strip bumper structureof FIG. 5 taken through the line 4-4;

[0026]FIG. 5 shows a schematic view of a second embodiment of a sweepforming assembly of the present invention;

[0027]FIG. 6 shows a partial sectional end view of the sweep formingassembly of FIG. 5;

[0028]FIG. 7 is a schematic side plan view of an assembly line thatincludes the sweep forming assembly;

[0029]FIG. 8 is a perspective view of an exemplary individual bumpermember;

[0030] FIGS. 9-14 show in fragmentary cross section outer peripheries ofa series of pairs of roll forming rollers of a roll forming assembly anda metal strip structure therebetween; and

[0031]FIGS. 15 and 16 show two views of a plurality of roller members ofthe sweep forming assembly of FIG. 1 in isolation flexing a bumperstructure at a point of flexure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] Referring to FIG. 7, the sweep forming assembly 10 is preferablyincluded as part of an assembly line 23 that includes a series ofassemblies which cooperate to produce a plurality of individual vehiclebumpers starting from a coiled strip structure of raw metal material.The cooperating assemblies uncoil and progressively shape the stripstructure into a continuous metal strip bumper structure and then cutthe continuous structure at regular intervals to form individual bumpermembers.

[0033] The assembly line 23 includes an uncoiling assembly 25 thatreceives and uncoils a roll of a metal strip structure made of a rawmetal material. The coiled portion of the metal strip structure isdesignated 27 and the uncoiled metal strip structure is generallydesignated 28. The portion of the metal strip structure 28 exiting theuncoiling assembly 25 passes sequentially through a plurality ofassemblies including a temper mill assembly 29, a stock straightenerassembly 31, an optional pre-pierce press assembly 33 and a roll formingassembly 37.

[0034] The uncoiling assembly 25, temper mill assembly 29 and stockstraightener assembly 31 uncoil, flatten and condition the metal stripstructure 28 so that the portion 21 thereof acted on by these assemblies25, 29, 31 forms a continuous, essentially flat blank that enters theroll forming assembly 37. The roll forming assembly 37 includes aplurality of pairs of roll forming rollers, generally designated 39,which progressively shape a transverse cross section in a longitudinallyextending portion of the blank metal strip structure 28. The portion ofthe metal strip structure 28 exiting the roll forming assembly 37 has apredetermined transverse bumper cross section and is generally referredto as a strip bumper structure, generally designated 53. The bumperstructure 53 generally includes (a) an initially shaped or formedportion 41 and (b) a initially shaped or formed portion 49. Theinitially shaped portion 41 has the predetermined roll formed transversebumper cross sectional configuration and an essentially straightlongitudinal configuration at the position of exit 43 of the rollforming assembly 37. Thus, the roll forming assembly 37 provides thecontinuous longitudinally extending initially shaped bumper structure 41at the position of exit 43 thereof and the initially shaped bumperstructure 41 moves downstream from there into the sweep forming assembly10.

[0035] Preferably, the sweep forming assembly 10 shown schematically inFIG. 7, is positioned on the assembly line 23 immediately downstream ofthe roll forming assembly 37. The sweep forming assembly 10 receives theinitially shaped continuous bumper structure 41 at the position of exit43 of the roll forming assembly 37 and provides a predeterminedlongitudinal bumper curvature to the initially shaped bumper structureto give the bumper structure its final form. The predeterminedtransverse cross section is not changed by the sweep forming assembly10. The finally formed portion 49 of the continuous bumper structure 53is fed into a cutoff press assembly 45 that the strip bumper structure53 into individual bumper members. An exemplary individual bumper member47 is shown in isolation in FIG. 8.

[0036] Preferably, the initially shaped bumper structure entering thesweep forming assembly 10 is roll formed to have a predeterminedtransverse cross section that includes 25. one at least partially openside. Two exemplary roll formed bumper structures having one at leastpartially open side are shown in cross section in FIGS. 3 and 4.

[0037]FIG. 3 shows the predetermined transverse bumper cross section ofthe exemplary bumper structure 53 (and of the bumper member 47), whichhas an open cross section. It can be understood that both the initialshaped and finally shaped portions 41, 49 of the 30 bumper structure 53(and the bumper member 47) have essentially the same cross section sothat the discussion of the cross section applies to all three 41, 47,49. The bumper structure 53 has transversely outwardly extending wallportions 32, 34 on opposite sides thereof and a roll formed recess 35.The roll formed recess 35 is defined by a central wall portion 36 andside wall portions 38, 40. The central wall portion 36 has an innersurface 42 and an outer surface 44. The recess 35 generally defines anopen side 46 of the cross section. The cross section of the bumperstructure 53 is referred to as “open” because the opposite transversewall portions 32, 34 extend generally away from the recess 35 leavingthe central recess 35 open.

[0038]FIG. 4 shows an exemplary cross-sectional view of thepredetermined cross section of an initially shaped bumper structure 74of an exemplary bumper structure generally designated 75 that has apartially closed cross section. The bumper structure 75 has transverselyinwardly extending wall portions 76, 78, a central wall portion 80 andside wall portions 82, 84. The central wall portion 80 has an innersurface 86 and an outer surface 88. The wall portions 76, 78 extendgenerally inwardly in spaced overlying relation to the central wallportion 80, thereby partially closing the cross section and providingthe cross section with a “C” shape. The bumper structure 75 thus has apartially open side, generally designated 92, that includes an opening90.

[0039] The sweep forming assembly 10 can be advantageously used toprovide bumper sweep to either a bumper structure having an opentransverse cross section (such as the exemplary bumper structure 53) orto a bumper structure having a partially open cross section (such asexemplary bumper structure 75).

[0040] Furthermore, a bumper structure having either an open orpartially open cross section can be swept in either of two generaldirections to provide a finally formed bumper structure that has eitheran inside sweep or an outside sweep. A finally formed bumper structureis considered to have inside sweep if its radius of curvature isdirected outwardly from the inner surface thereof 42 or 86,respectively. The exemplary bumper member 47 shown in FIG. 8 has aninside sweep. Similarly, a finally formed bumper structure is consideredto have an outside sweep if its radius of curvature is directedoutwardly from the outer surface thereof 44 or 88, respectively.

[0041] As will become apparent, the sweep forming assembly 10 of thepresent invention can be constructed and operated to provide a bumperstructure having an open cross section with either an inside or anoutside predetermined bumper curvature (i.e., bumper sweep) or toprovide a bumper structure having a partially open cross section witheither an inside or outside predetermined bumper curvature.

[0042] The rollers 39 of a roll forming assembly 37 are spaced toreceive the metal strip structure 28 therebetween and that theperipheries of the rollers 39 are constructed to progressively shape thetransverse cross section. FIGS. 9-14 show the peripheries of upper andlower roller of the series of pairs of rollers 39 of the toll formingassembly 37. The complementary pairs of rollers are designated ³ 9 a and39 b; 39 c and 39 d; 39 e and 39 f; 39 g and 39 h; 39 i and 39 j; and 39k and 39 l. It can be appreciated that when the roll forming assembly 37is configured to form a strip bumper structure having an open crosssection, the outer peripheries of each pair of rollers 39 are generallyof complimentary male and female configuration. The pairs of rollers 39are arranged so that the portion of the strip structure 28 extendingthrough the roll forming assembly 37 is at a constant vertical height.This vertical height is referred to as the “line level” of the rollforming assembly 37. The initially shaped continuous bumper structure 41(see FIG. 7) emerges from the position of exit 43 of the roll formingassembly 37 at line level.

[0043] FIGS. 1-2 show a sweep forming assembly, generally designated 10,constructed according to the principles of the present invention. Thesweep forming assembly 10 generally includes a base 12, a primarycarriage assembly 14, a driven support member 16, first and seconddriven flexing rollers 18, 20 and an auxiliary roller 22.

[0044] A fragmentary portion of the bumper structure 53 is showninterengaged with the sweep forming assembly 10. The downstreamdirection in FIGS. 1 and 2 is from right to left, as indicated by astraight directional arrow on the right hand side of each of FIGS. 1 and2 (spaced slightly above the initially shaped portion 41 of the bumperstructure 53).

[0045] The driven support roller 16 and the first driven flexing roller18 are mounted on the base 12 of the sweep forming assembly 10 forrotational movement with respect thereto. The base 12 is a metalstructure, preferably made of steel, and includes a bottom plate 84 anda pair of upwardly extending, essentially vertical wall plates 86 fixedto the plate 84. The wall plates 86 are affixed to the plate 84 intransversely spaced, parallel relation to support the rollers 16, 18 andthe primary carriage assembly 14 therebetween in a manner describedbelow. The wall plates 86 are preferably reinforced by horizontallyextending top plate fixed between upper portions of wall plates 86. Thewall structure 89 is also preferably also made of steel.

[0046] The driven support roller 16 and the first flexing roller 18 areaffixed to respective shafts 88, 90. Each end of the shaft 88 isrotatably mounted in a gear box 92 and each gear box 92 is, in turn,mounted in a respective wall plate 86 of the base 12. Similarly, eachend of the shaft 88 is rotatably mounted in a gear box 94 and each gearbox 94 is, in turn, mounted in a respective wall plate of the base 12.Thus, the shafts 88, 90 define the rotational axes of the respectiverollers 16, 18.

[0047] The primary carriage assembly 14 is pivotally mounted generallybetween the wall plates 86 on the shaft 90 for pivotal movement withrespect to the base 12. Thus, the axis of rotation of the first flexingroller 18 is coaxial with the pivot axis of the primary carriageassembly 14. The primary carriage assembly 14 is a metal structure,preferably made of steel and includes a carriage bottom plate 100 and apair of wall plates 102 affixed to the carriage bottom plate 100. Thewall plates 102 are affixed to the bottom plate 100 in transverselyspaced, parallel relation and cooperate to support the second drivenflexing roller 20 and portions of an auxiliary carriage assembly 110therebetween.

[0048] The second flexing roller 20 is fixedly mounted on a shaft 106.The shaft 106 is rotatably mounted between the wall plates 102 of theprimary carriage assembly 14.

[0049] As can be appreciated from a comparison of FIGS. 1 and 2, whenthe primary carriage assembly 14 is pivoted with respect to the base 12,the second flexing roller 20 moves with the primary carriage assembly 14such that pivotal movement of the primary carriage assembly with respectto the base 12 causes pivotal movement of the second flexing roller 20with respect to the first flexing roller 20 about the pivot axis definedby shaft 90. The inter-axial distance between the axes of rotation(defined by shafts 90, 106) of the first and second driven flexingrollers 18, 20 is a fixed distance in all positions of pivotaladjustment of the primary carriage assembly 14 with respect to the base12.

[0050] Preferably, the rollers 16, 18, 20 are driven. Specifically, thefirst and second flexing rollers 18, 20 drive the bumper structure 53 inthe downstream direction. The support roller 16 supports an upstreamportion of the bumper structure to resist downward movement of thebumper structure 53 during the flexing operation. Driving the supportroller 16 minimizes the resistance to the movement of the bumperstructure 53 in the downstream direction.

[0051] Outer gears 160, 162 are affixed on respective shafts 88, 90 indriving relation to the associated rollers 16, 18. Each drive gear 160,162 is engaged through a chain drive (not shown) or other appropriatestructure with a source of mechanical power (not shown). Secondary drivegears 164, 166 are fixedly mounted on respective shafts 90, 106 so thatdriven movement of the outer gear 162 drives both secondary gears 164,166 and thus both rollers 18, 20.

[0052] A primary carriage adjustment assembly 124 is operatively mountedbetween the base 12 and the primary carriage assembly 14 to pivot theprimary carriage assembly 14 with respect to the base 12 and to hold theprimary carriage assembly 14 in an adjusted operating positionthereafter. The adjustment assembly 124 includes a housing 126 fixed tothe bottom plate 84 of the base 12 and a lower portion of a verticallyextending threaded shaft 128 is rotatably mounted in the housing 126. Acontrol assembly 130 is operatively engaged with the threaded shaft 128to control rotation of the threaded shaft 128 with respect to thehousing 126.

[0053] The threaded shaft 128 extends through an opening in the bottomplate 100 of the primary carriage assembly 14 and between a pair ofsupport wall plates 131 fixed to the bottom plate 100 on oppositetransverse sides of the opening in the plate 100. A threaded member 132is pivotally mounted between the wall plates 131 by pivot shafts 133. Anupper end of the threaded shaft 128 threadedly engages the threadedmember 132. Bidirectional rotation of the threaded shaft 128 causesbidirectional threaded movement of the threaded member 132 along theshaft 128. Threaded movement of threaded member 132 along the shaft 128causes pivotal movement of the primary carriage assembly 14 with respectto the base 12. The threaded engagement between the shaft 128 and thethreaded member 132 holds the primary carriage assembly 14 in anadjusted operating position with respect to the base 12 when rotationalmovement of the shaft 128 ceases.

[0054] The adjustment assembly 137 is operatively mounted between theprimary carriage assembly 14 and the auxiliary carriage assembly 110 tocontrol movement of the auxiliary carriage assembly with respect to theprimary carriage assembly 14. Specifically, a lower end of a threadedshaft 136 is rotatably mounted in a housing 138 mounted on the bottomplate 100. An upper end of the threaded shaft 136 threadedly engages athreaded member 140 mounted to the mounting plate 112. Rotation of thethreaded shaft 136 with a control assembly (not shown) causes slidingmovement of the auxiliary carriage assembly 110 (through the range ofmovement provided by the slots 113 and bolts 111) with respect to theprimary carriage assembly 14 to raise and lower the roller 22 withrespect to the first and second flexing rollers 18, 20. Threadedengagement between the shaft 136 and the member 140 hold the auxiliarycarriage assembly in an adjusted operating position with respect to theprimary carriage assembly 14 after rotation of the shaft 136 ceases.

[0055] The auxiliary carriage assembly 110 is movably mounted on theprimary carriage assembly 14, generally between the wall plates 102. Theauxiliary carriage assembly 110 is a metal structure, preferably made ofsteel and includes an auxiliary mounting plate 112 and a pair of wallplates 114 affixed to the mounting plate 112. The wall plates 114 areaffixed to the mounting plate 112 in transversely spaced, parallelrelation and cooperate to rotatably support the auxiliary roller 22therebetween.

[0056] The auxiliary carriage assembly 110 is mounted for relativemovement with respect to the primary carriage assembly 14 by bolts 111that extend through elongated slots 113 formed in the mounting plate 112of the auxiliary carriage assembly 110. Specifically, a series of bolts111 is mounted in each wall plate 102 of the primary carriage assembly14, each bolt 111 extending through a slot 113. Movement of theauxiliary carriage assembly 110 with respect to the primary carriageassembly 14 provides relative movement of the auxiliary roller 22 withrespect to the first and second flexing rollers 18, 20. The auxiliarycarriage assembly 110 is moved with respect to the primary carriageassembly 14 and is held in an adjusted operating position with respectthereto by an adjustment assembly 137.

[0057] An optional exit roller assembly 119 which includes a pair oftransversely spaced exit rollers 120 is mounted to the mounting plate112 of the auxiliary carriage assembly 110. The exit rollers 120 areidler rollers that rotate about shafts 122. The exit rollers 120 supportopposite transverse edges of the bumper structure 53 when the same iscut in the cut off press 45 which is preferably positioned immediatelydownstream of the sweep forming assembly 10 (see FIG. 7). The exitrollers 120 are thus not involved in the sweep forming operation but canbe mounted on the assembly 10 as a convenience to the bumpermanufacturer. Preferably the exit roller assembly 119 is movably mountedon the mounting plate 112 by bolts or other appropriate structure sothat its position can be changed to accommodate a wide range of sweepcurvatures.

[0058] The manner in which the pivotal position of the primary carriageassembly 14 with respect to the base 12 is adjusted can be understoodfrom a comparison if FIGS. 1 and 2.

Operation

[0059] The sweep forming assembly 10 is constructed and arranged toreceive at the position of exit 43 of a roll forming assembly 37 theinitially shaped roll formed bumper structure 41 constructed of a metalmaterial and having a predetermined roll formed transverse bumper crosssection and a substantially straight longitudinal configuration and toimpart a permanent bumper curvature to the bumper structure, therebyproviding the finally shaped bumper structure 49 downstream of the sweepforming assembly 10.

[0060] The driven support roller 16 supports bumper structure 53 at theposition of exit of the roll forming assembly 37. The first and seconddriven flexing rollers 18, 20 drive the bumper structure 53 in thedownstream direction and are positioned downstream of the driven supportroller 16 sufficiently close to flex the bumper structure 53 at a pointof flexure 143 between the driven support roller 16 and the first andsecond driven flexing rollers 18,20.

[0061] Preferably, the support roller 16 and the first flexing roller 18are mounted on the base 12 such that the uppermost point of an outerperiphery 146 of the first flexing roller 18 is vertically higher thanthe line level. In the sweep forming assembly 10, the shafts 88, 90 areat the same vertical height. The vertical height differential betweenthe peripheries 146, 148 is achieved by making the radius of the firstflexing roller 18 greater than the radius of the support roller 16.Preferably the outer periphery 148 of the driven support roller 16 is atline level and the outer periphery 146 of the first flexing roller 18 isapproximately 2.5 cm (one inch) above line level. Thus, the firstflexing roller 18 provides a small amount of lift or deflection to thebumper structure 53 as it passes thereover.

[0062] Alternatively, the height differential between the outerperipheries 146, 148 can be achieved by having a support roller and afirst flexing roller of equal radius and mounting the respective shaftson the base so that the shaft of the first flexing roller is verticallyhigher than the vertical height of the shaft of the driven supportroller.

[0063] Generally, to provide sweep to the bumper structure 53, anassembly operator pivots or revolves the second flexing roller 20 in aflexing direction (clockwise from the point of view of FIGS. 1, 2, 15and 16) using the control assembly 130 of the primary carriageadjustment assembly 124 as previously described. The pivotal movement ofthe primary carriage assembly 14 revolves the second flexing roller 20about the pivot axis defined by shaft 90 with respect to the firstflexing roller 18. FIG. 1 shows the second flexing roller 20 (andtherefore the primary carriage assembly 14) in a first pivotal positionwith respect to the first flexing roller 18 and FIG. 2 shows the secondflexing roller 20 in a second pivotal position with respect to the firstflexing roller 18. As is considered in more detail below, FIGS. 15 and16 also illustrate the pivotal movement of the second flexing roller 20in the flexing direction with respect to the first flexing roller 18 andshows the rollers 16, 18 and 20 in isolation.

[0064] Pivotal or revolving movement of the second flexing roller 20 inthe flexing direction exerts a force on the bumper structure whichflexes the same at the point of flexure 143 between the first flexingrollers 18 and the support roller 16. As can be appreciated from acomparison of FIGS. 1 and 2 (and of 15 and 16), the greater the pivotalmovement of the carriage assembly 14 in the flexing direction, thegreater the degree of flexure and thus the greater the degree ofpermanent curvature imparted to the metal material of the bumperstructure 53.

[0065] The flexing action of the bumper structure 53 at the point offlexure 143 can be best understood from a comparison of FIGS. 15 and 16which shows the rollers 16, 18 and 20 in isolation. FIG. 15 shows thesecond flexing roller 20 in a first position of pivotal adjustment withrespect to the first flexing roller 18 and FIG. 16 shows the secondflexing roller 20 in a second position of adjustment after having beenpivoted about the axis of rotation of the first flexing 18 in theflexing direction (indicated in FIGS. 15 and 16 by a directional arrowextending outwardly from the axis of rotation of the second flexingroller 20).

[0066] The flexing rollers 18, 20 are in driving engagement with theportion of the bumper structure 53 between their outer peripheries 146,150. It can be understood that the portion of the bumper structure 53that is between the peripheries 146, 150 of the flexing rollers 18, 20at any moment is essentially tangent to the peripheries 146, 150 and istherefore essentially perpendicular to an imaginary line drawn betweenthe axes of rotation defined by the shafts 90, 106 of the rollers 18, 20(this imaginary line is represented by a dashed line in FIGS. 15 and16). Movement of the second flexing roller 20 in the flexing directionmoves the imaginary line in a clockwise direction about the axis definedby the shaft 90 and consequently shifts the point of driving engagementof the bumper structure and the outer peripheries 146, 150 of the drivenflexing rollers 18, 20 in a clockwise direction about the outerperiphery 146 of the first flexing roller 18. Thus, pivotal movement ofthe second flexing roller 20 changes the direction of travel of theportion of the bumper structure between the flexing rollers 18, 20 suchthat the greater the movement of the second flexing roller 20 in theflexing direction, the steeper the slope of the path traveled by thebumper structure between the peripheries 146, 150. The support roller 16is close enough to the first flexing rollers 18 such that the bumperstructure flexes at a point between therebetween in response to thepivotal or revolving movement of the second flexing roller 20 in theflexing direction.

[0067] It is now apparent to those skilled in the art that the supportroller 16 must be positioned sufficiently close to the flexing rollers18 to cause flexure of the metal material beyond the elastic limitthereof in response to the pivotal movement of the support roller 20. Ifthe support roller 16 were positioned a relatively large distance fromthe flexing rollers 18, 20, movement of the second flexing roller 20 inthe flexing direction would not generate a sufficient force topermanently curve the bumper structure, particularly when a highstrength steel is used in the bumper structure construction.

[0068] If the support roller 16 were on one assembly or station and thefirst and second flexing rollers 18, 20 were on a second assembly orstation, they would not be positioned close enough to flex the metalmaterial a sufficient degree to impart a significant degree of permanentlongitudinal curvature, particularly when a high strength metal is usedto construct the bumper structure. It can also be understood thatbecause the support roller 16 supports the portion of the bumperstructure immediately upstream of the first and second flexing rollersin opposition to the flexing force exerted by the rollers 18, 20, it isusually not necessary that the support roller 16 be paired with an upperroller.

[0069] With reference again to FIGS. 15 and 16, it can be appreciatedthat the greater the clockwise movement of the second flexing rollerabout the pivot axis defined by shaft 90, the greater the degree ofbumper structure flexure and therefore the greater the degree ofpermanent longitudinal curvature. Generally, the flexing rollers 18, 20flex the metal material of the bumper structure 53 at a point 143slightly upstream of the point of driving engagement between the bumperstructure 53 and the flexing rollers 18, 20. It can be appreciated thatthe exact location of this point of flexure changes as the angularposition of the support roller 18 with respect to the flexing roller 20changes.

[0070] The sweep forming assembly 10 is configured to provide the bumperstructure 53 with an inside sweep. Thus, the open cross section bumperstructure 53 emerges from the exemplary roll forming assembly 37 in theorientation shown in FIG. 3 with the inside surface 42 facing upwardly.It can be understood that the bumper structure 53 could be rotated 180degrees and the sweep forming assembly 10 reconfigured in a mannerdescribed below if it was desired to sweep the bumper structure 53 inthe outside direction.

[0071] The outer peripheries of the rollers 16, 18, 20 and 22 are shapedto conform to the respective facing sides of the bumper structure 53.Specifically, the outer peripheries 146, 150 of the flexing rollers 18,20 are of complementary male and female configuration and areessentially the same in profile as the roll forming rollers 39 k and 39l of FIG. 14 and conform to the respective sides of the bumper structure53 in surface-to-surface driving engagement therewith. As mentioned, theinter-axial distance between the shafts 90, 106 is fixed. Therefore, theradial distance between the outermost peripheries 146 and 150 of thefirst and second driven flexing rollers 18 and 20 is constant in allpivotal positions of adjustment of the second roller 20 with respect tothe first flexing roller 18. Preferably this inter-periphery distance isapproximately equal to the thickness of the metal of the bumperstructure 53. Since the outer peripheries 146, 150 of the first andsecond flexing rollers 18, 20 conform to the associated sides of thebumper structure, the bumper structure can be flexed to a high degree bythe action of the rollers 18, 20 without crushing or otherwise deformingthe predetermined transverse bumper cross section during the sweepingforming operation. More particularly, the outer peripheries 146, 150support the transverse cross section and protect it from being crushedor otherwise deformed during the flexing operation.

[0072] A high degree of bumper curvature can be imparted to a bumperstructure 53 through angular adjustment of the second flexing roller 20relative to the first flexing roller 18. The degree of curvature dependsupon a number of factors, including the modulus of elasticity of themetal material of the bumper structure 53, the thickness of the metalmaterial and the cross sectional configuration of the bumper structure.However, there may be a limit to the degree of curvature that can beimparted to a particular bumper structure using the flexing rollers, 18,20 and the support roller 16. Excessive pivotal movement of the secondflexing roller 20 in a flexing direction may nonetheless cause a tearingor uncontrolled puckering of the wall portions of the bumper structure53. The side wall portions 38, 40 (see FIG. 3) are particularlysusceptible to deformation or tearing during sweep forming.

[0073] The auxiliary roller 22 can be used to increase of the degree ofsweep imparted to a bumper structure 53 beyond that which can beachieved using the rollers 16, 18, 20 alone. The auxiliary roller 22 ispreferably an idler roller. The auxiliary roller 22 is positioneddownstream of the first and second driven flexing rollers such that theportion of the bumper structure 53 driven downstream by the flexingrollers 18, 20 is driven into the auxiliary roller to bend the bumperstructure 53 beyond the elastic limit of the metal material.

[0074] To increase the curvature of the bumper structure 53 using theauxiliary roller 22, the operator adjusts the position of the auxiliarycarriage assembly 110 with respect to the primary carriage assembly 14using the adjustment assembly 137 as aforesaid to move the roller 22upwardly into engagement with the downwardly facing side of the bumperstructure 53. FIG. 1 shows the auxiliary roller 22 spaced slightly belowand thus out of engagement with the bumper structure 53. FIG. 2 showsthe auxiliary roller 22 (and auxiliary carriage assembly 110) movedupwardly with respect to the primary carriage assembly 14 and shows theauxiliary roller 22 in engagement with the bumper structure 53.

[0075] The length 155 of the bumper structure 53 between the first andsecond flexing rollers 18, 20 and the auxiliary roller 22 is bent as therollers 18, 20 drive the bumper structure 53 into the auxiliary roller22. It has been found that this bending can impart an increased amountof sweep to a given bumper structure beyond that imparted by the flexingoperation alone. Flexure imparted to the bumper structure 53 at thepoint of flexure 143 by the flexing rollers 18, 20 imparts a firstdegree of permanent curvature to the bumper structure 53 and theauxiliary roller 22 imparts a second degree of permanent curvature tothe bumper structure 53.

[0076] An advantage of the sweep forming assembly 10 is that bothcarriage assemblies 14, 110 can be adjusted while the sweep formingassembly 10 is operating. Thus, the sweep forming assembly 10 can beadjusted “on-the-fly”. This capability allows the operator to monitorthe condition of the bumper structure 53 exiting from the sweep formingassembly 10 as the operator is adjusting the same.

[0077] If, for example, the second flexing roller 20 is pivoted too farin the flexing direction, thereby causing the wall portions of theparticular bumper structure 53 to tear slightly or pucker uncontrollablybefore the desired degree of sweep is achieved, the operator can ‘backoff’ the second flexing roller 20 until no puckering and/or tearing isobserved. The operator can then further increase the amount of impartedsweep by moving the auxiliary roller 22 in the sweep increasingdirection to increase the degree of sweep.

[0078] It can be understood that because the operator is able adjust thepositions of the rollers 20, 22 while the assembly 10 is operating, theoperator is able to produce a wide range of settings on the sweepforming assembly 10. The flexing roller 20 and the auxiliary roller 22can be thought of as the “coarse” and “fine” adjustments, respectively,of the sweep forming assembly 10. The adjusting procedure followed for aparticular bumper structure can be varied to best impart sweep to theparticular bumper structure.

[0079] Driving the rollers 16, 18, 20 allows a greater degree of bumpercurvature to be imparted to the bumper structure 53 by the sweep formingassembly 10 compared to a sweep forming assembly with passive rollersbecause driving the bumper structure 53 prevents the same from bucklingas it passes through the sweep forming assembly 10. Pushing the bumperstructure in the downstream direction through the sweep forming assemblywould tend to cause the bumper structure to buckle and buckling deformsthe bumper structure, particularly the predetermined transverse bumpercross section. Driving the rollers 16, 18, 20 pulls the bumper structure53 through the sweep forming assembly 10, thereby preventing buckling.

[0080] The sweep forming assembly 10 provides the initially shapedbumper structure 41 emerging from the position of exit 43 of the rollforming assembly 37 with the desired degree of permanent bumpercurvature. As mentioned, after the initially shaped continuous bumperstructure 41 is provided with the desired amount of sweep, the bumperstructure 53 has achieved its final bumper shape. The bumper structure53 is then cut into individual bumper members, one of which is shown inFIG. 8 and generally designated 47.

[0081] The individual bumper members can be used to provide vehiclebumpers. Alternatively, one (or more) bumper members can be mounted to abumper mounting structure to close the one at least partially open sideof each bumper member to form a bumper beam assembly having a closedcross section. The method of mounting one or more individual bumpermembers on a mounting structure to form a bumper beam assembly having aclosed cross section is disclosed in the commonly assigned U.S. PatentApplication Serial No. 60/100,835 which application is herebyincorporated by reference into the present application for all materialdisclosed therein.

[0082] A sweep forming assembly for providing bumper sweep to aninitially shaped bumper structure having a partially closed crosssection is represented in FIGS. 5 and 6 and is generally designated 210.The construction and operation of sweep forming assembly 210 is similarto that of sweep forming assembly 10. The sweep forming assembly 210 isshown schematically in FIG. 5 to show the differences between theassemblies 10, 210 more clearly.

[0083] A driven support roller 216, a first and a second driven flexingroller 218, 220, respectively, and an auxiliary roller 222 of theassembly 210 are shown in isolation FIG. 5. The general structure andoperation of the base, the primary carriage assembly, the auxiliarycarriage assembly and associated structures of the sweep formingassembly 210 and the manner in which the rollers 216, 218, 220 and 222are mounted on the same are essentially identical to that shown (seeFIGS. 1 and 2) and described above for the sweep forming assembly 10.Consequently, the base, carriage assemblies and associated structuresare omitted from the FIG. 5. Portions of the sweep forming assembly 210that are identical to portions of the sweep forming assembly 10 areidentified by identical reference numerals and are not describedfurther. The gears 164, 166 are shown in dashed lines to more clearlyshow the structure of the associated rollers.

[0084] The main difference between the sweep forming assemblies 10, 210is that when a bumper structure having a partially closed cross section(such as exemplary bumper structure 75 shown in FIG. 4) is sweep formedin the sweep forming assembly 210, a pair of snake arbors 230 areprovided in the interior the bumper structure 75, one arbor 230 on eachtransverse side of the bumper structure. Opposite ends of the arbors 230are secured to bracket members 232, 233 (fragments of which are shown inFIG. 5 and one of which is shown in FIG. 6) which extend through theopening 90 of the bumper structure 75. An upper end portion of thebracket member 232 is preferably secured to structure on the auxiliarycarriage assembly 238 (shown in end view in FIG. 6). The bracket member233 is preferably mounted to the base. Two pairs of tie rods 244 aresecured between the brackets 232, 233 (one pair on each side of thebumper structure 75) and a series of blocks 246 are mounted on the rods.

[0085]FIG. 6 shows a partial view of the sweep forming assembly 210looking into the exit of the assembly 210 in the upstream direction. Thefirst flexing roller 218 engages substantially the entire outsidesurface of the bumper structure 75. The second flexing roller 220includes lateral roller portions 250 of lesser radius which rollinglyengage upper exterior edges 252 of the bumper structure 75 and a centralroller portion 254 of greater radius which extends through the opening90 in the predetermined cross section and engages a central portion ofthe surface 86 of the interior of the bumper structure 75. Thus, a snakearbor 230 extends on each side of the central portion 254 of the secondflexing roller 220. The snake arbors 230 and brackets 232 slidinglyengage inside surfaces of the bumper structure 75. Alternatively, thearbors 230 and/or the brackets 232 can be constructed to include aplurality of rollers (not shown) constructed and arranged to rollinglyengage upwardly and downwardly facing interior surfaces 86 and 255,respectively, of the cross-section.

[0086] Each bumper structure is preferably formed from strips of rawsheet metal material, preferably steel. One preferred steel for use withthe sweep forming assembly 10 is a martinsitic steel having a KSI ofbetween approximately 190 (referred to as a martinsitic 190) toapproximately 220 (referred to as a martinsitic 210) (or an MPa ofbetween 1310 and 1516). These steels are readily commercially availableand are referred to respectively by the trade names “Inland M190” and“Inland M220” steel. The martinsitic 190 and the martinsitic 220 arequenched and tempered steels characterized by minimum ultimate tensilestrengths of 190,000 and 220,000 psi, respectively (1310 MPa and 1516MPa, respectively). Both the martinsitic 190 and the martinsitic 220have a grain structure comprised entirely of tempered martinsite.

[0087] Another preferred steel for use with the sweep forming assembly10 is a dual-phase 140T quenched and tempered steel. This steel isreadily commercially available and is referred to by the trade name“Inland Di-Form 140T” steel. The dual-phase 140T is characterized by aminimum ultimate tensile strength of 140,000 psi, (965 MPa) and has agrain structure comprised of ferrite and tempered martinsite.

[0088] Another preferred steel for use with the sweep forming assembly10 is a High Strength Low Alloy (HSLA) 120XF steel. Although this steelis referred to as “High Strength Low Alloy”, it is not actually one ofthe High Strength Low Alloy grades; it is referred to as being “HighStrength Low Alloy”, however, because it is manufactured by a similarprocess. The HSLA 120XF is characterized by a minimum 0.2% offset yieldstrength of 120,000 psi (827 MPa) and has an entirely ferritic grainstructure. This steel is readily commercially available and is referredto by the trade name “LTV 120 XF steel”.

[0089] These steels are preferably used to manufacture individual bumpermembers that each have a uniform steel wall thickness. Preferably thebumper members are constructed of a steel having a strength of at leastapproximately 120 KSI (827 MPa) and more preferably are constructed of asteel having a strength greater than about 180 KSI (1240 MPa).

[0090] For example, a bumper can be constructed of a roll formed metalmaterial by providing an elongated roll formed bumper member having apredetermined transverse bumper cross section and a longitudinal extent,the predetermined transverse bumper cross section having one at leastpartially open side, and the longitudinal extent having a predeterminedbumper curvature of from about zero to about eighty and the metalmaterial having a KSI of at least 120 (827 MPa). Preferably, the metalmaterial is a steel that has a minimum 0.2 percent offset yield strengthof about 120,000 psi (827 MPa) and an entirely ferritic grain structure.More preferably, the metal material is a quenched and tempered steelhaving a minimum ultimate tensile strength of about 140,000 psi (965MPa) and a grain structure comprised of ferrite and tempered martinsite.Most preferably, the metal material is a quenched and tempered steelhaving a minimum ultimate tensile strength of from about 190,000 toabout 220,000 psi (from about 1310 MPa to about 1516 MPa) and having anentirely tempered martinsite grain structure. When a steel having astrength of at least approximately 180 KSI (1240 Mpa) is used in theconstruction, the preferred steel wall thickness of the bumper member iswithin the range of from about 0.8 mm to about 1.6 mm, and is morepreferably within the range of from about 1.0 mm to about 1.3 mm. When asteel having a KSI of approximately 120 to approximately 180 (827 to1240 MPa) is used in the construction, the wall thickness of each bumpermember is preferably approximately 2.0 mm. The sweep forming assemblies10, 210 can be constructed and operated to provide a wide range ofinside or outside bumper sweep to initially shaped bumper structuresconstructed of a wide range of metal materials having a wide range ofbumper cross sections. It is within the scope of the invention toproduce a bumper member constructed of any of the metal materialsdescribed herein having either an open or closed cross section andhaving a bumper sweep of up to 80 or higher.

[0091] It can be appreciated that the description of the constructionand operation of the sweep forming assembly is exemplary only, and notintended to limit the scope of the invention. For example, a sweepforming assembly can be constructed according to the principles of thepresent invention which provides inside or outside bumper sweep of over80. Embodiments are contemplated and have been constructed which providesweep as high as approximately 155.

[0092] It is also within the scope of the present invention to provide adriven mating roller vertically spaced above the driven support roller16 when relatively high degrees of sweep (above approximately 80, forexample) are being provided to an initially shaped bumper structure, orwhen the thickness of the metal material is relatively high or both. Ithas been found that the additional roller provides greater stability tothe bumper structure during the sweep forming operation.

[0093] Similarly, the description of the metal materials used in bumperconstruction and the descriptions of bumper construction are intended toillustrate the invention and are not intended to limit the scope of theinvention. Materials having properties outside the ranges describedherein are also contemplated to be used in bumper construction. Forexample, steel having a hardness below 120 (827 Mpa) can be swept on asweep forming assembly constructed according to the principles describedherein.

[0094] Similarly, the bumper cross sections described and illustratedare exemplary and are intended to illustrate general types of crosssections and not to limit the range of bumper structures that can beswept using the sweep forming assembly or to limit the bumper membersconstructed according to the principles of the present invention tomembers having specific cross sections.

[0095] While the invention has been disclosed and described withreference with a limited number of embodiments, it will be apparent thatvariations and modifications may be made thereto without departure fromthe scope of the invention. Therefore, the following claims are intendedto cover all such modifications, variations, and equivalents thereof inaccordance with the principles and advantages noted herein.

What is claimed is:
 1. A method for producing a roll formed bumpercomprising of a metal material and having a predetermined transversecross section and a predetermined curvature, said method comprising:feeding a bumper structure (40) into a forming assembly (10) along aline level, said bumper structure having said predetermined transversecross section and an essentially straight longitudinal configuration,said forming assembly comprising a driven support roller (16) and a pairof driven cooperating flexing rollers (18, 20), a first roller (18) ofsaid pair of flexing rollers positioned to deflect said bumper structureout of said line level and a second roller (20) of said pair of flexingrollers mounted to revolve about said first roller, simultaneouslydriving said support roller and counter-rotating said pair ofcooperating flexing rollers for feeding said bumper structure betweensaid pair of cooperating flexing rollers, and revolving said secondflexing roller about said first flexing roller to flex said bumperstructure between said support roller and said first flexing rollerthereby imparting a permanent longitudinal curvature to the bumperstructure.
 2. A method as claimed in claim 1 wherein by varying a degreeof revolving of said revolving step, the permanent curvature imparted tosaid bumper structure (40) is responsively varied.
 3. A method asclaimed in claim 2 wherein said permanent longitudinal curvature is saidpredetermined curvature.
 4. A method as claimed in claim 2 wherein saidforming assembly further comprises an auxiliary roller (22), saidauxiliary roller being positionable to engage said bumper structure (40)as said bumper structure exits from between said pair of cooperatingrollers (18, 20), said method further comprising a step of moving saidauxiliary roller relative to said first flexing roller (18) to flex saidbumper structure about said second flexing roller thereby imparting afurther permanent longitudinal curvature to said bumper.
 5. A method asclaimed in claim 4 wherein said further permanent longitudinal curvatureis said predetermined curvature.
 6. A method as claimed in claim 5wherein said method further comprises a step of cutting said bumperstructure (40) to a desired length providing a plurality of bumpermembers (47) having said predetermined curvature.
 7. A bumperconstructed of a roll formed metal material, comprising an elongatedroll formed bumper member (47) having a predetermined transverse crosssection and a longitudinal extent, said predetermined transverse crosssection having one at least partially open side, said bumper beingcharacterized in that said longitudinal extent hasa predetermined bumpersweep of about 80 and said metal material having an MPa of at least 827.8. A bumper as claimed in claim 7 wherein said metal material is amartinsitic steel.
 9. A bumper as claimed in claim 8 wherein said metalmaterial is a steel that has a minimum 0.2 percent offset yield strengthof about 120,000 psi (827 MPa) and a ferritic grain structure.
 10. Abumper as claimed in claim 9 wherein said bumper member has a thicknessof less than approximately 2.0 mm.
 11. A bumper as claimed in claim 7wherein said metal material is a quenched and tempered steel having aminimum ultimate tensile strength of about 140,000 psi (965 MPa) and agrain structure comprised of ferrite and tempered martinsite.
 12. Abumper as claimed in claim 11 wherein said bumper member has a thicknessof less than approximately 2.0 mm.
 13. A bumper as claimed in claim 7wherein said metal material is a quenched and tempered steel having aminimum ultimate tensile strength of from about 190,000 to about 220,000psi (from about 1310 MPa to about 1516 MPa) and having a temperedmartinsite grain structure.
 14. A bumper as claimed in claim 13 whereinsaid bumper member has a thickness within the range of approximately 0.8mm to approximately 1.6 mm.
 15. A bumper as claimed in claim 14 whereinsaid bumper member has a thickness within the range of approximately 1.0mm to approximately 1.3 mm.
 16. A sweep forming assembly (10)comprising: a driven support roller (16) positioned to receive a stripbumper structure (40) at a line level; and a driven first flexing roller(18) positioned to deflect said bumper structure from said line leveland a driven second flexing roller (20) cooperating with said firstflexing roller for counter rotating therewith, said second flexingroller movably mounted to revolve about said first flexing roller, andan adjustment assembly (137) operably engaging said second flexingroller (20) to effect said revolving movement of said second flexingroller about said first flexing roller (18), said revolving movementeffecting engagement of said second flexing roller with said bumperstructure between said support roller (16) and said first flexing roller(18) and urging said bumper structure (40) thereagainst imparting apermanent longitudinal curvature to the bumper structure.
 17. A sweepforming assembly (10) as claimed in claim 16, said assembly furtherincluding an auxiliary roller (22) movably mounted to move relative tosaid first flexing roller (18) and an auxiliary adjustment assembly(110) operably engaging said auxiliary roller to effect said relativemovement, said relative movement effecting engagement of said auxiliaryroller with said bumper structure (40) to urge the bumper structureabout said second flexing roller imparting a further longitudinalcurvature to the bumper structure.
 18. A sweep forming apparatus asclaimed in claim 17 wherein said rollers (16, 18, 20, 22) arecomplementarily shaped to engage said bumper structure (40) in a face toface relationship.
 19. A sweep forming apparatus as claimed in claim 18wherein said apparatus further comprises an arbor (230) engaging andsupporting an interior of said bumper structure.